The present invention relates to mixtures of solid materials and fuel oil and, in particular, to a process and apparatus used in preparing mixtures of fuel oil and micronized solid carbonaceous materials.
It has been suggested that, for boiler use and certain other purposes, currently limited supplies of fuel oil might be appreciably extended by mixing such fuel oil with more abundant solid carbonaceous fuels such as coal, coke, petroleum coke, graphite, or charcoal. While such mixing can significantly increase the heat value of a given amount of fuel oil, it has been found that, in order to produce a physically stable carbon-oil mixture having a suitable degree of reactivity, the solid carbonaceous material must be reduced to micron or submicron size before mixing takes place. As might be expected, the reduction of the solid carbon to such a small size, especially in the amounts which would be necessary for the large scale production of carbon-oil mixtures, is an expensive and cumbersome procedure. These high costs are attributable not only to the sizeable initial investment required for the necessary transport and pulverizing equipment, but also to the rapid wearing of that equipment and to the occurrence of certain adverse environmental effects which accompany the employment of the carbon-oil mixture production processes currently in use. For example, reduction of coal and other solid carbonaceous materials for the purpose of producing carbon-oil mixtures is commonly accomplished in fluid mills in which expensive, high quality steam is employed. Such mills experience rapid erosion by the jet streams. Furthermore, the steam effluent leaving the process carries superfine carbon particles, thus necessitating the installation of additional expensive equipment for the purpose of removing these particles from the steam.
U.S. Pat. No. 2,612,320 discloses a pulverizer in which particles are impacted against one another by means of a plurality of fluid streams. This pulverizer requires that pulverized particles be removed from an enclosed impact area by suction, and while certain features are disclosed which tend to limit undesirable accumulations of particles in the impact area, the fact that such accumulations are still possible and that relatively elaborate apparatus is necessary to effect their removal must be considered a disadvantage of this design. Furthermore, where pulverization occurs as a result of collisions between particles in intersecting fluid streams, there exists a probability that a certain number of particles will escape such collisions. Consequently, since there is no second grinding stage in the apparatus disclosed in U.S. Pat. No. 2,612,320, that design may require an undesirably high percentage of particles to be recycled for further pulverization.
U.S. Pat. No. 251,803, on the other hand, discloses an impact pulverizer in which all particles to be pulverized are entrained in a fluid stream and then impacted against a rotating, conically shaped concussion plate. The rotating concussion plate not only pulverizes the particles but also imparts lateral motion to them so as to continuously remove pulverized particles from the impact area. While this design avoids some of the above-mentioned disadvantages attending the design disclosed in U.S. Pat. No. 2,612,320, it is possible that rapid wearing of the grinding surface of the concussion plate will occur since most, if not all, required pulverization occurs on that surface. The lack of any appreciable action which might serve to augment the pulverizing occuring on the grinding surface may be attributable to the small probability that a significant number of destructive collisions will occur between unreduced particles in the fluid stream before they have impacted against that grinding surface.
Consequently, it is found that, notwithstanding the great potential for conserving scarce supplies of fuel oil which the widespread use of carbon-oil mixture might have, such widespread acceptance of this fuel has not been achieved, in large part due to the aforementioned difficulties associated with its production. It is, therefore, an object of the present invention to provide a process and apparatus for the production of carbon-oil mixtures by which these difficulties are substantially overcome.